Fire alarm system



p 1962 H. o. MOORE I 3,056,122

FIRE ALARM SYSTEM Filed June 10. 1959 2 Sheets-Sheet 1 HARRY O- M00125INVENTOR. 16 23 sYiJmp eflfi -udf I l 2 I ATTORNEYS Sept. 25, 1962 H. o.MOORE FIRE ALARM SYSTEM Filed June 10, 1959 2 Sheets-Sheet 2 BY ,fi 4

ATTORNEY United States Patent M 3,056,122 FIRE ALARM SYSTEM Harry 0.Moore, 2921 Rozzells Ferry Road, Charlotte, N. C. Filed June 10, 1959,Ser. No. 819,356 8 Claims. (Cl. 340-232) This invention relatesgenerally to improvements in fire alarm systems, and more particularlyto improvements in fire alarm systems of the type suitable for use in adwelling structure or home.

Although fires annually cause extensive losses of life and property soas to create a desire for providing a reliable fire alarm system indwelling structures, such as houses, apartments, etc., this desire haslargely remained unsatisfied mainly because of the expenses involved ininstalling conventional commercial fire alarm systems in homes.Simplified fire alarm systems employing highly combustible materials asfuses to set off fire alarm devices have been developed for use in thehome, but have not been favorably received by the home-owner, possiblybecause of the hazards inherently presented through the use of suchcombustible fuses which themselves may be the cause of fires. A commonfailing in these conventional home fire alarm systems exists in theirrelative lack of sensitivity to an abrupt increase in heat, a factorwhich allows a fire to gain a good head-way before the alarm is actuatedto alert the occupant of the dwelling structure to the presence of thefire. In such instances, attempts by an occupant to put out the fire arefutile or at least greatly hampered when the fire has been allowed todevelop in intensity and to rage uncontrolled.

Perhaps the largest incidence of destruction of life and property byfires in the home occurs during the fall and winter months when coldertemperatures require the operation of a furnace for heating the home.This is partly explainable because of the consumption of a combustiblefuel by the furnace when in operation. The fire upon reaching the fuelflowing into an operating furnace quickly develops in intensity as itconsumes the fuel and may become virtually uncontrollable. In addition,the heat from the fire on the furnace may create a highly explosivecondition because of the resulting vaporization and/or expansion of thefuel flowing into the furnace.

It is an object of this invention to provide an improved fire alarmsystem utilizing an alarm device, which may be in the form of a bell,interposed in an electrical alarm circuit having a normally open switchtherein, and the switch being held in open position by a taut strand ofthermoplastic material extending throughout a room or rooms in thebuilding structure. The thermoplastic strand is highly sensitive to anabrupt increase in heat so as to part upon a fire being started torelease the switch allowing it 'to close and complete the alarm circuitfor actuating the alarm device.

It is another object of this invention to provide an improved fire alarmsystem cooperating with the electrical circuit for operating a furnacein a dwelling structure, wherein the alarm device in the fire alarmsystem is actuated in response to an abrupt increase in heat caused bythe starting of a fire while the electrical circuit for the furnace isbroken to shut olf the furnace and reduce the dangers which would beinherently presented by the continued flow of fuel to the furnace if thefurnace remained in operation.

It is another object of this invention to provide in a fire alarm systemhaving an electrical alarm circuit with an alarm device disposed thereinand switch means in the alarm circuit, a strand of thermoplasticmaterial normally holding the switch means open and being attached to afurnace damper to prevent the damper from closing the 3,056,122 PatentedSept. 25, 1962 air intake opening of the furnace. Upon a fire breakingout in the vicinity of the thermoplastic strand, the thermoplasticstrand will part allowing the switch means to close the alarm circuitand the damper to close the air intake opening of the furnace, therebyactuating the alarm device and eventually causing the fire in thefurnace to be smothered by blocking the air intake opening.

Some of the objects of the invention having been stated, other objectswill appear as the description proceeds when taken in connection withthe accompanying drawings, in which-- FIGURE 1 is a schematicperspective view illustrating the fire alarm system embodying thepresent invention as being installed in a room, such as a basement orcellar in a dwelling structure;

FIGURE 2 is a diagrammatic view illustrating the wiring of the firealarm system shown in FIGURE 1 with the back wall of the switch removed;

FIGURE 3 is a sectional view of the switch utilized in the fire alarmsystem, taken substantially along the line 3-3 in FIGURE 2;

FIGURE 4 is an elevational view of a furnace, parts thereof being shownin phantom lines for purposes of clarity, illustrating a modified formof fire alarm system associated therewith;

FIGURE 5 is a fragmentary horizontal sectional View taken along the line55 in FIGURE 4;

FIGURE 6 is an enlarged fragmentary vertical sectional view, taken alongline 66 in FIGURE 4;

FIGURE 7 is an enlarged horizontal sectional view of the switch meansutilized in the modified fire alarm system, taken along line 77 inFIGURE 4; and

FIGURE 8 is a diagrammatic view illustrating the wiring of the modifiedfire alarm system and showing the switch means in vertical section, astaken along line 88 in FIGURE 7.

Referring more specifically to the drawings and to FIGURE 2particularly, there is illustrated means for connecting the fire alarmsystem to the existing source of electrical current in a dwellingstructure, this means being shown in the form of an electrical connectorplug 10. From the plug 10, a pair of electrical conductors or wires 11,12 extend to a bell transformer 13 to supply electrical current thereto.The bell transformer 13 is of a conventional step-down type, designed tosupply six (6) volts to an alarm device 14 through wires 15, 16extending between the bell transformer 13 and the alarm device 14-.

The alarm device 14 preferably takes the form of a bell, as shown, thebell preferably being installed in a room likely to be inhabited duringthe major portion of a day. It is contemplated that the fire alarm bell14 may also be the front door bell of the dwelling structure or could beinstalled at a convenient outside location so as to warn not only theinhabitants of the dwelling structure but also their neighbors in theevent that the dwelling structure is unoccupied at the time when a firebreaks out. A light signal (not shown) may be incorporated with thealarm bell 14 to give a visual alarm, if desired.

A switch means 20 is interposed in one of the wires 15, 16 extendingbetween the transformer 13 and the alarm device 14, FIGURE 2illustrating the switch means 20 as being interposed in the wire 16. Thedetails and functioning of the switch means 20 will be subsequentlydescribed.

The electrical plug 10* also includes a second pair of wires 21, 22extending therefrom, the wires 21, 22 forming an electrical circuit foroperating the electric motive means, hereinafter referred to as a motor23, of a furnace 24. It will be observed that the Wire 21 leads directlyfrom the plug 10 to one terminal of the motor 23, while the wire 22 isinterrupted by the disposition of the switch 3 means 20 therein so as toform an indirect connection between the plug and the other terminal ofthe motor 23.

The details of the switch assembly 20* will now be described. The switchmeans 20 is of a double-throw type and comprises a flanged back wall 24which is adapted to be aflixed to a wall of the dwelling structure bysuitable means and a casing or switch housing 25 having side walls andtop and bottom walls frictionally received by the flanged back wall 24to enclose the operating parts of the switch means 20. A pair of spacedswitch contact members 26, 27 are suitably mounted within the confinesof the switch housing 25 on the front wall thereof. It will be observedthat a layer of insulation material, such as rubber, is sandwichedbetween each of the switch contact members 26, 27 and the wall surfaceof the switch housing 25 on which they are mounted as a precautionarymeasure to prevent the switch housing 25 from becoming electrified. Thespaced switch contact members 26, 27 may take any desirable form, beingL- shaped as shown to present spaced parallel legs or contacts 30, 31extending away from the front wall of the switch housing 25.

A switch arm or lever 32 is mounted in the switch housing 25 for pivotalmovement about one of its ends. The opposite end of lever 32 extendsbetween the contacts 30, 31 of the switch contact members 26, 27,respectively. The pivotal mounting of the switch lever 32 may beaccomplished in any desired manner, such as by mounting one end of theswitch lever 32 about the shank of a screw 33 protruding from the frontwall within the interior of the switch housing 25, the shank of thescrew 33 being loosely received in a bore provided in the end of switchlever 32, as shown in FIGURE 2. The switch lever 32 preferably includesan integral leg 34 extending transversely from the end thereof looselyreceiving the screw 33. It will be observed that a counterweight 35 isprovided on the end of the leg 34 remote from the pivotally mounted endof switch lever 32 for a purpose to be subsequently described.

A pair of contact plates 36, 37 are provided on opposite sides of theswitch lever 32 at locations in alinement with the contacts 30, 31,respectively. The switch lever 32 is insulated from the contact plates36, 37 by a suitable layer of insulation material, such as rubber,sandwiched between each of the contact plates 36, 37 and thecorresponding side of the switch lever 32. A resilient means in the formof a coiled compression spring 40 biases the switch lever 32 about itspivot point in a clockwise direction, as viewed in FIGURE 2. The coiledspring 40 is seated between one of the side walls of the switch housing25 and a medial position on the switch lever 32, cup-like elements 41,42 being secured to the switch housing 25 and the switch lever 32,respectively, to receive opposite ends of the coiled compression spring40.

It will be observed that each of the contacts 30, 31 and the plates 36,37 is provided with a single terminal thereon for connection to anelectrical conductor or wire in the fire alarm system. In thisconnection, contact 30 and plate 36 are connected to the adjacentterminal portions of the segments comprising wire 22 which extendsbetween the plug 10 and the motor 23 for the furnace 24, while contact31 and plate 37 are connected to the adjacent terminal portions of thesegments comprising wire 16 which extends between the bell transformer13 and the fire alarm device 14. It will be apparent, therefore, thatengagement between the contact 30 and plate 36 will complete theelectrical circuit through the motor 23 of the furnace 24 to supplycurrent to the motor for operating the furnace, while engagement betweenthe contact 31 and plate 37 will complete the electrical alarm circuitto actuate the alarm device 14 therein. The switch lever 32 is movableabout its pivot point so as to effect alternative engagement between thetwo sets of switch elements 30, 36 and 31, 37, each set comprising acontact and a plate, respectively. From the foregoing, it will beunderstood that the electrical circuit for the motor 23 of the furnace24 and the electrical alarm circuit for the fire alarm device 14 arenever completed at the same time. Normally, the switch lever 32 will beheld in a position wherein the contact plate 36 thereon engages contact30 to complete the electrical circuit through the motor 23 of furnace24, this being accomplished by a heat-fusible strand 43 of thermoplasticmaterial, such as nylon or polyethylene, one end of which is attached tothe end of the witch lever 32 opposite from the pivotally mounted end ina suitable manner. The thermoplastic strand 43 is disposed about a roomin a dwelling structure which is infrequently occupied, such as abasement, cellar or attic, FIGURE 1 illustrating the strand 43 as beingthreaded through a plurality of eye-bolts 44 depending from the beams 45of a basement ceiling. The eyebolts 44 are preferably arranged todistribute the thermoplastic strand 43 in such a manner as to cover alarge area of the room. A weight 46, such as a sandbag or the like, isattached to the other end of the thermoplastic strand 43 to maintain itin a taut position so as to pull the switch lever 32 in acounter-clockwise direction, thereby compressing spring 40 and effectingengagement between the contact 30 and plate 36.

The thermoplastic strand 43 is very susceptible to an abrupt increase ofheat and will part at a point or points therealong upon a fire beingstarted in the vicinity thereof. In this respect, tests were conductedwith strands of nylon and high-tenacity polyethylene as compared to astrand of cotton, wherein the strands were held in a taut conditionabove the flame from a match. The nylon and polyethylene strands readilyparted, but the cotton strand remained intact and did not part until itwas lowered relative to the flame. Because of the high tensile strengthof nylon and polyethylene strands as contrasted to that of a cottonstrand, a nylon or polyethylene strand when employed as thethermoplastic strand 43 in the present invention can be of a filamentousnature, while a cotton strand would necessarily be somewhat bulky inorder to withstand the tension placed thereon without breaking. Thenylon and polyethylene strands thus exhibited high heat sensitivity andhigh tensile strength. These factors coupled together in the strand 43employed in the fire alarm system result in a marked degree ofsensitivity of the fire alarm system to the presence of a fire.

A single break in the thermoplastic strand 43 relieves the switch lever32 from the pull exerted thereon by the weight 46, whereupon thecompressed coil spring 40 is permitted to expand while thecounter-weight 35 tends to fall downwardly. The conjoint action of thecoil spring 40 and the counter-weight 35 causes the switch lever 32 topivot in a clockwise direction to effect engagement 'between the contact31 and plate 37, while breaking the engagement between the contact 30and plate 36. The provision of the counter-weight 35 on the leg 34 ofthe switch lever 32 insures that the switch lever 32 will move in aclockwise direction upon a parting of the thermoplastic strand 43, eventhough the coil spring 40 may have become permanently deformed orcrystallized in its compressed state due to remaining in its compressedstate over a long period of time.

Upon clockwise movement of the switch lever 32 being effected asdescribed herein, the electrical alarm circuit is completed by theengagement between the contact 31 and plate 37 to actuate the alarmdevice 14 which warns of the presence of a fire. At the same time, theelectrical circuit through the motor 23 of the furnace 24 is broken bythe disengagement of the contact 30 and plate 36 to stop the operationof the furnace 24 and accordingly eliminate the danger presented by thecontinuous flow of fuel into the furnace 24 if the furnace 24 remainedin operation.

Referring now more particularly to FIGURES 4-8, inclusive, a modifiedform of the fire alarm system is shown- Reference characters with theprime notation added will be used to designate elements similar to thosefound in the fire alarm system disclosed in FIGURES 1-3, inclusive.Thus, FIGURE 8 shows an electrical connector plug 10 for connecting themodified fire alarm system to the existing source of electrical currentin the dwelling structure. From the plug 10', a pair of electricalconductors or wires 50, 51 extend to a bell transformer 13' to supplyelectrical current thereto, the bell transformer 13' being for the samepurpose described in connection with bell transformer 13 of FIGURES 1-3,inclusive, that isto supply six (6) volts to an alarm device 14 throughwires 52, 53. A switch means is interposed in the wire 53 extendingbetween the transformer 13 and the alarm device 14'.

It will be observed that the wires 50, 51 across which the primary coilof the 'bell transformer 13 is connected form an electrical circuit foroperating the electric motive means, hereinafter referred to as motor23', of a furnace 24'.. The wire 50 leads directly from the plug 10' toone terminal of the motor 23', while the wire 51 is interrupted by thedisposition of the switch means 20' therein so as to form an indirectconnection between the plug 10 and the other terminal of the motor 23.

The switch means 20' in the modified fire alarm system comprises aswitch housing or casing 55 adapted to be afiixed to an outer wallsurface of the furnace 24' and having a cover or lid 56 received thereonso as to enclose the operating components of the switch means 20' withinthe switch housing 55. Within the confines of the switch housing 55,there is a first switch unit 57 which comprises a closed tube or vial 60having one end loosely mounted about a pin 61 attached to a bracketmember 62 (FIG- URE 7). The bracket member 62 is secured to the backwall of the switch housing 55. The vial 60 is free to pivot about thepin 61. The terminal portions of the segments comprising wire 51 extendinto the vial 60 in spaced apart relationship to provide a break in theelectrical circuit for the motor 23. A globule of mercury M is containedwithin the vial 60 and is adapted to bridge the gap between the adjacentterminal ends of the segments comprising wire 51 to complete theelectrical circuit through the motor 23 for the furnace 24'. The firstswitch unit 57, hereinafter termed a mercury switch, isnormallymaintained in the position shown in-FIGURE 8, wherein the mercuryglobule M bridges the gap between the adjacent terminal ends of thesegments comprising wire 51 by means to be subsequently described.

A second switch unit 66 is also contained within the switch housing 55,the second switch unit 66 being disposed in the wire 53 forming part ofthe electrical alarm circuit through the alarm device 14". As shown, thesecond switch unit 66 [is of the push-button type and comprises a switcharm 67 having a contact 68 on its lower surface and a push-button 69 onits upper surface, the switch arm 67 being mounted in the switch housing55 for pivotal movement about its end remote from the contact 68. Astationary switch element 70 having a contact 71 thereon opposed to thecontact 68 on the switch arm 67 is mounted in spaced relationship withrespect to the switch arm 67; Resilient means in the form of a spring 72is interposed between the pivotal switch arm 67 and the stationaryswitch element 70 to normally maintain the contacts 68, 71 carriedthereby in spaced apart relationship. It will be observed that thepivotal switch arm 67 is connected'to the terminal portion of onesegment of wire 53, while the stationary switch element 70 is connectedto the terminal portion of the other segment of Wire 53.

The switch means 20" is adapted to be interposed in a suitably insulatedtubular member 74 which extends vertically along an outer wall surfaceof the furnace 24'. The tubular member 74 receives one terminal portionof a thermoplastic strand 43' which is intended to be disposedthroughout a room or rooms of the dwelling 6 structure in a mannersimilar to that disclosed in FIGURE 1. It will be observed that theportion of the thermoplastic strand 43' in the tubular member 74 alsoextends through the switch housing 55, suitable openings being providedin the switch housing 55 for that purpose, and is attached to a damperelement 75 for the air intake opening 76 of the furnace 24.

The damper element 75 is mounted for slidable movement along the outerwall surface of the furnace 24 for opening and closing the air intakeopening 75 of the furnace 24. In this connection, a pair of spacedangleiron brackets 77 extending vertically along opposite sides of theair intake opening 75 may be aflixed to the outer wall surface of thefurnace 24 to provide oppositely disposed slots or trackways forslidably receiving the side edges of the damper element 75. In normaloperation, the damper element 75 is held in the position shown in FIGURE6 by the thermoplastic strand 43' under the pull of a weight (notshown), such as the weight 46 shown in FIGURE 1, thereby uncovering theair intake opening 76 to permit air to be drawn into the furnace 24' forallowing proper combustion of the fuel being burned thereby.

It will be observed in FIGURE 8 that the thermoplastic strand 43 isprovided with a collar member 80 of rigid material securely afiixedtherearound and located within the switch housing 55. A stop means inthe form of a pin 81 extends forwardly from the back wall of the switchhousing 55. The mercury switch 57 includes an aperture 82 through thevial 60, the aperture 82 being located in the end thereof remote fromthe pivotally mounted end. The modified fire alarm system disclosed inFIGURES 4-8, inclusive, is cocked or readied for operation by passingthe thermoplastic strand 43 through the aperture 82, in the vial '60 ofthe mercury switch 57 so as to dispose the collar member'St) on thethermoplastic strand 43 below the vial 611', while the pin 81 isdisposed above the vial 60. The thermoplastic strand 43' is maintainedin a tautcondition by a weight (not shown), such as the weight 46 shownin FIGURE 1, which pulls the collar member 80 upwardly against the vial66 of the mercury switch 57 to pivot the vial 60 in a counter-clockwisedirection until the vial abuts the pin 81. At the same time, the damperelement 75 is drawn upwardly in the angle-iron brackets 77 to uncoverthe air intake opening 76 of the furnace 24'. The men: cury globule Maccordingly shifts within the vial 60 to a position wherein it spans thegap between the adjacent terminal portions of the segments comprisingwire 51 to complete the electrical circuit through the motor 23 for thefurnace 24'. When the mercury switch 57 is in closed position, as shownin FIGURE 8, the push-button switch 66 is open and thereby holds theelectrical alarm circuit through the alarm device 14 open because of theinterruption in the wire 53 extending between the bell transformer 13'and the alarm device 14'.

Upon a fire breaking out in the vicinity of the thermoplastic strand 43,the strand 43' parts at a point or points therealong to release theupward pulling force of the collar member 80 on the switch 57. When thevial 60 of the mercury switch 57 is no longer drawn upwardly against theretaining pin 31 by the collar member 80, it pivots downwardly about pin61 in a clockwise direction to cause the mercury globule M to shift itsposition therein which breaks the circuit through the motor 23' for thefurnace 24'. The vial 60 strikes the button 69 on the pivotal switch arm67 and forces the switch arm 67 downwardly in a clockwise directionagainst the biasing force of spring 72 to a position wherein thecontact68 on the switch arm 67 engages the opposed contact 71 on thestationary switch element to close the electrical alarm circuit foractuating the alarm device 14'. Meanwhile, the parting of thethermoplastic strand 43' also releases the damper element which slidesdownwardly in the angle-iron brackets 77 to close the air intake opening76 of the furnace 24.

In effect, therefore, the parting of the thermoplastic strand 43 by thepresence of a fire in the room in which the thermoplastic strand 43' islocated causes three separate safeguards in the modified fire alarmsystem to be actuated: (1) The electrical alarm circuit itself iscompleted to sound the alarm device 14' for warning occupants of thedwelling structure of the fire; (2) The electrical circuit through themotor 23 for the furnace 24 is broken, thereby shutting ofi the furnace24'; and (3) the air intake opening 76 for the furnace 24 is closed bythe damper element 75 which will eventually result in the fire withinthe furnace 24' being smothered to stop the operation of the furnace24'. The shutting off of the furnace 24' whenever a fire breaks out in aroom of the dwelling structure eliminates the hazard inherently incidentupon continued operation of the furnace 24- by a constant flow ofcombustible fuel thereinto. It will be understood that such control ofthe furnace 24- insures that a fire which has broken out in the dwellingstructure will not be fed by fuel flowing into the furnace 24', nor willthe fire within the furnace 24' be permitted to escape its confines.

There have been disclosed improved fire alarm systems of a type suitablefor use in a dwelling structure, the fire alarm systems being highlysensitive and accurate in operation, while relatively inexpensive incost and free from maintenance.

In the drawings and specification there has been set forth a preferredembodiment of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being defined in theclaims.

I claim:

1. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said electrical alarm circuit, an electrical circuit foroperation of a furnace, switch means interposed in said alarm circuitand said furnace circuit, said switch means comprising a housing, aswitch lever pivotally mounted in said housing and having contact plateson opposite sides thereof electrically connected in said furnace circuitand said alarm circuit respectively, and a pair of spaced apart contactsfixed in said housing on opposite sides of said switch lever inalinement with said contact plates carried thereon, one of said fixedcontacts being disposed in said furnace circuit and the other in saidalarm circuit, and a heatfusible strand attached to said switch leverand holding said switch lever in a position wherein said plate thereonand said fixed contact in the furnace circuit are in engagement forclosing said furnace circuit and opening said alarm circuit, and meansto pivot said switch lever to a position wherein said plate thereon andsaid fixed contact in the alarm circuit are in engagement for openingsaid furnace circuit and closing said alarm circuit in response to aparting of said strand for shutting off the furnace and actuating saidalarm device.

2. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said electrical alarm circuit, an electrical circuit foroperation of a furnace, switch means interposed in said alarm circuitand said furnace circuit, said switch means comprising a housing, aswitch lever pivotally mounted in said housing and having contact plateson opposite sides thereof electrically connected in said furnace circuitand said alarm circuit respectively, and a pair of spaced apart contactsfixed in said housing on opposite sides of said switch lever inalinement with said contact plates carried thereon, one of said fixedcontacts being disposed in said furnace circuit and the other in saidalarm circuit, and a heatfusible strand attached to said switch leverand holding said switch lever in a position wherein said plate thereonand said fixed contact in the furnace circuit are in engagement forclosing said furnace circuit and opening said alarm circuit, and acompression spring seated between said switch lever and said housing,said spring expanding to pivot said switch lever to a position whereinsaid plate thereon and said fixed contact in the alarm circuit are inengagement for opening said furnace circuit and closing said alarmcircuit in response to a parting of said strand for shutting off thefurnace and actuating said alarm device.

*3. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said alarm circuit, switch means interposed in said alarmcircuit and operable to close said alarm circuit, a heat-fusible strandattached to said switch means and holding said switch means in aposition opening said alarm circuit, a furnace having an air intakeopening, a damper mounted on said furnace for movement between positionsopening and closing the air intake opening, said strand being secured tothe damper to normally restrain said damper in a position opening theair intake opening, said switch means being movable to a positionclosing said alarm circuit and said damper being movable to a positionclosing the air intake opening in said furnace in response to a partingof said strand for actuating said alarm device and stopping the intakeof air by the furnace.

4. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said alarm circuit, switch means interposed in said alarmcircuit and operable to close said alarm circuit, a heat-fusible strandattached to said switch means, means maintaining said strand in apre-arranged manner extending over a wide area, and means stretchingsaid strand taut for holding said switch means in a position openingsaid alarm circuit, a furnace having an air intake opening above which adamper is slidably mounted, said strand being secured to the damper torestrain said damper against downward movement, said switch means beingmovable to a position closing said alarm circuit and said damperdescending to cover the air intake opening in said furnace in responseto a parting of said strand for actuating said alarm device and stoppingthe intake of air by the furnace.

5. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said alarm circuit, an electrical circuit for operation of afurnace, switch means interposed in said alarm circuit and said furnacecircuit and operable to alternatively close said furnace circuit andsaid alarm circuit, a heat-fusible strand attached to said switch meansand holding said switch means in a position closing said furnace circuitand opening said alarm circuit, a furnace having an air intake opening,a damper mounted on said furnace for movement between positions openingand closing the air intake opening, said strand being secured to thedamper to normally restrain said damper in a position opening the airintake opening, said switch means being movable to a position openingsaid furnace circuit and closing said alarm circuit and said damperbeing movable to a position closing the air intake opening in saidfurnace in response to a parting of said strand for shutting off thefurnace. actuating said alarm device and stopping the intake of air bythe furnace.

6. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said electrical alarm circuit, an electrical circuit foroperation of a furnace, switch means interposed in said alarm circuitand said furnace circuit, said switch means comprising a first switchunit movable between open and closed positions in said furnace circuitand a second switch unit being normally open to hold said alarm circuitopen, a heat-fusible strand, and means on said strand bearing againstsaid first switch unit and holding said first switch unit in a positionclosing said furnace circuit, said first switch unit shifting to openposition in response to a release of said means bearing thereagainstcaused by a parting of said strand and engaging said second switch unitto close said second switch unit for completing the alarm circuit andactuating the alarm device while opening said furnace circuit to shutoff the furnace.

7. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said electrical alarm circuit, an electrical circuit foroperation of a furnace, switch means interposed in said alarm circuitand said furnace circuit, said switch means comprising a mercury switchhaving a vial mounted for pivotal movement between open and closedpositions, said mercury switch being disposed in said furnace circuit,and a push-button switch having a movable contact and a fixed contactnormally maintained in spaced relationship, said push-button switchbeing disposed in said alarm circuit, a heat-fusible strand attached tosaid vial of the mercury switch and holding said vial in closed positionto complete said furnace circuit, and said vial of the mercury switchbeing pivotable to open position breaking said furnace circuit andengaging said push-button switch to force said movable contact intoabutment with said fixed contact for closing said alarm circuit inresponse to a parting of said strand for shutting oft the furnace andactuating said alarm device.

8. In a fire alarm system, an electrical alarm circuit, an alarm devicedisposed in said electrical alarm circuit, an electrical circuit foroperation of a furnace, switch means interposed in said alarm circuitand said furnace circuit, said switch means comprising a mercury switchhaving a vial mounted for pivotal movement between open and closedpositions, said mercury switch being disposed in said furnace circuit,and a push-button switch having a movable contact and a fixed contactnormally maintained in spaced relationship, said push-button switchbeing disposed in said alarm circuit, a heat-fusible strand, a collarmember afiixed on said strand and bearing against said vial of themercury switch to hold said vial in closed position to complete saidfurnace circuit, a furnace operated by said furnace circuit and havingan air intake opening, a damper slidably mounted on said furnace abovethe air intake opening, said strand being secured to the damper torestrain said damper against downward movement, and said vial of themercury switch being pivotable to open position breaking said furnacecircuit and engaging said push-button switch to force said movablecontact into abutment with said fixed contact for closing said alarmcircuit and said damper descending to cover the air intake opening insaid furnace in response to a parting of said strand releasing saidcollar member from bearing against said vial of the mercury switch forshutting off the furnace, actuating said alarm device and stopping theintake of air by the furnace.

References Cited in the file of this patent UNITED STATES PATENTS1,176,809 Barton Mar. 28, 1916 1,225,437 Hammond May 8, 1917 1,633,923Casey June 28, 1927 2,290,047 Hildebrecht July 14, 1942 2,470,711 MobergMay 11, 1949 2,540,527 Ingels Feb. 6, 1951 2,567,112 Kagan Sept. 4, 1951FOREIGN PATENTS 555,268 Great Britain Aug. 13, 1943

